Bulk Enhancement For Airlaid Material

ABSTRACT

An airlaid substrate may have a positive increase in thickness through the addition of thermally expandable microspheres into the substrate. In one application, the substrate may be converted to sheets used as wet or dry wipes.

The present invention generally relates to a method of incorporating thermally expandable microspheres into a material so that the resulting products have increased bulk. More particularly, the present invention is directed to the incorporation of thermally expandable microspheres into an airlaid material.

BACKGROUND OF THE INVENTION

Most consumers have a perception that the thickness of a non-dispersible or dispersible wipe is related to hand protection and cleaning. Specifically, it is thought that thicker airlaid sheet products provide better hand protection and cleaning effect. In the current technology, the addition of a binder into a sheet of an airlaid substrate causes the substrate to collapse in the z-direction, and thus reducing the stack thickness. Therefore, it is desirable to recover the thickness of an airlaid substrate to improve consumer perception.

SUMMARY OF THE INVENTION

It has now been discovered that the thickness reduction in airlaid substrates can be reversed by adding a thermally expandable thermoplastic microspheres to a formed sheet of airlaid material. Thermally expandable microspheres are spherically formed particles with a gas-proof shell encapsulating a drop of liquid hydrocarbon. When exposed to heat, the microsphere volume expands about 50 times. The thermally expandable microspheres can be used for bulk enhancement of dispersible moist wipes and other airlaid-based products.

In one aspect of the invention there is a sheet of airlaid material made from fibers and having a thickness. There is a plurality of thermally expandable microspheres distributed at least partially into the material thickness. A binder material is applied to the sheet to keep the microspheres in place.

In another aspect of the invention is a method of making an airlaid sheet having a thickness, the method including the steps of: (a) spraying an airlaid sheet with a bonding material; and (b) spraying the thermally expandable microspheres onto the airlaid sheet.

In yet another aspect of the invention is a method of making an airlaid sheet including the step of incorporating the thermally expandable microspheres into a forming station along with fibers for airlaying so that the airlaid sheet has thermally expandable microspheres distributed at least partially through the sheet thickness prior to spraying the sheet with a binder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscopic (SEM) view of a cross section of a wetted airlaid substrate (a control).

FIG. 2 is a plan view of the wetted airlaid substrate of FIG. 1.

FIG. 3 is a SEM view of a cross section airlaid substrate showing the distribution of expanded thermally-expandable microspheres within the substrate.

FIG. 4 is a plan view of the airlaid substrate of FIG. 3.

FIG. 5 is a schematic representation of one embodiment of an airlaying forming station.

FIG. 6 is a schematic representation of an airlaying process suitable for making the substrate of the present invention as formed in FIG. 5.

DETAILED DESCRIPTION OF THE ENCLOSED EMBODIMENTS

Reference now will be made in detail to the embodiments of the invention, and the examples of which are set forth below. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment.

Thus, it is intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents. Other features and aspects of the present invention are disclosed in the following detailed description. Examples of commercial products that are being produced via air forming include but are not limited to industrial wipers, disposable hospital underpads, disposable tablecloths and napkins, pre-moistened baby wipes, and absorbent cores for diapers, feminine pads and the like.

One aspect of the present invention is an airlaid substrate for wet wipes that is treated with a binder and thermally activated microspheres. When heated, the microsperes expand thereby causing the airlaid substrate to expand in the z-direction (thickness). The result of the expansion is added bulk which gives the consumer a better hand feel and the perception that the wet wipes are more apt to clean better.

Airlaid Substrate

“Airlaying” is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 3 to about 52 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air to activate a binder component or a latex adhesive. Airlaying is taught in, for example, U.S. Pat. No. 4,640,810 to Laursen et al.

The production of airlaid nonwoven composites is well defined in the literature and documented in the art. Examples include the DANWEB process as described in U.S. Pat. No. 4,640,810 to Laursen et al assigned to Scan Web of North America Inc; the Kroyer process as described in U.S. Pat. No. 4,494,278 to Kroyer et al. and U.S. Pat. No. 5,527,171 to Soerensen assigned to Niro Separation a/s; the method of U.S. Pat. No. 4,375,448 Appel et al. assigned to Kimberly-Clark Corporation, or other similar methods. The webs produced by these methods may subsequently be bonded together to form an adequate tensile strength web by thermal fusing, latex bonding or combinations thereof, which are well known in the art. Webs produced in this text are best exemplified but not limited to the DANWEB process.

The fibrous material may be formed from a single layer or multiple layers. In the case of multiple layers, the layers are generally positioned in a juxtaposed or surface-to-surface relationship and all or a portion of the layers may be bound to adjacent layers. The fibrous material may also be formed from a plurality of separate fibrous materials wherein each of the separate fibrous materials may be formed from a different type of fiber. In those instances where the fibrous material includes multiple layers, the binder composition of the present invention may be applied to the entire thickness of the fibrous material, or each individual layer may be separately treated and then combined with other layers in a juxtaposed relationship to form the finished fibrous material.

Airlaid nonwoven fabrics are particularly well suited for use as wet wipes. The basis weights for airlaid nonwoven fabrics may range from about 30 to about 350 grams per square meter (gsm) with staple fibers having a denier of about 0.5-10 and a length of about 6-15 millimeters. Wet wipe substrates may generally have a fiber dry density of about 0.025 g/cc to about 0.2 g/cc.

Bonding

Generally, there are three ways to bond fibers: (a) with an adhesive (b) thermally, or (c) a combination of adhesive and thermal bonding. Of the binders there are two types, namely, dispersible and non-dispersible binders. A non-dispersible adhesive binder, such as a latex adhesive, used on an airlaid substrate is used to create a cohesive web which does not disperse/degrade when exposed to water. A dispersible adhesive binder and optional dispersible cobinder composition (“binder(s)”) may be a component of a web which enhances bonding of the fibers and/or filaments within a nonwoven web to provide wet strength to a wet wipe or the like. The binder(s) composition for a dispersible wipe is desirably ion-sensitive such that in the presence of water it becomes soluble, thus allowing the nonwoven web to disperse.

Thermally activated binders can be used in airlaid structures to help provide mechanical integrity and stabilization. Such binders include fiber, liquid or other binder means that may be thermally activated. These binders may be dispersible or non-dispersible.

Without the presence of the thermally expanding microspheres of the present invention, these types of dispersible and non-dispersible binder(s) cause the substrate to collapse in the z-direction (a direction perpendicular to a plane defining a surface of the nonwoven web).

In some aspects, the total amount of dispersible adhesive binder(s) composition present in the nonwoven web can range from about 5 to about 65 wt %, such as between about 7 to about 35 wt %, or between about 10 to about 25 wt % or between about 15 to 20 wt % based on the total weight of the nonwoven web. A sufficient amount of the binder(s) composition results in a nonwoven web that has desirable in-use integrity, but quickly disperses when disposed in tap water.

One particular example of thermally activated binder fibers are polyolefin fibers. Lower melting point polymers, such as polyolefin polymers, provide the ability to bond the fabric together at fiber cross-over points upon the application of heat. In addition, fibers of a lower melting polymer, like conjugate and biconstituent fibers are suitable for practice of this invention. Fibers having a lower melting polymer are generally referred to as “fusible fibers.” By “lower melting polymers” what is meant are those fibers having a glass transition temperature less than about 175° C. Thermally activated fibers are available from many manufacturers such as Chisso of Tokyo, Japan and Fibervisions, L.L.C. of Wilmington, Del.

Regardless of the type of binder used, it is desirable that the binder(s) composition can be processed on a commercial scale (i.e., the binder(s) may be capable of rapid application on a large scale, such as by spraying). Further, the binder(s) composition can further provide acceptable levels of sheet wetability. In addition, it is desirable that all components of the wet wipe, including the binder(s) composition, are non-toxic and relatively economical.

Thermally Expandable Microspheres

The microspheres may be added anywhere in the manufacturing of the airlaid making process. For example, the microspheres may be added to the forming chamber in an airlaying forming station as described herein (see FIG. 5).

Many brands of microspheres may be utilized, such as AQUA SLURRY from Polytex Environmental Inks and MATSUMOTO MICROSPHERE from Matsumoto Yushi-Seiyaku Co., Ltd. One desireable brand of microspheres is sold under the name EXPANCEL by Akzo Nobel. In particular, EXPANCEL 091 DU 80 microspheres consist of hollow, white, spherically-formed polymer particles encapsulating a blowing agent (for example, liquid isobutane) under pressure. The EXPANCEL 091 DU 80 microspheres generally have a mean diameter of about 80 micrometers after expansion.

The density of the microspheres is about 1000-1300 kg/m³. The thermoplastic shell softens when heated so that the gasification of the blowing agent expands the microspheres to a final volume that is from 30 to more than 60 times larger than the original volume at constant weight. The density of the expanded microsphere is then below about 30 kg/m³.

The microspheres start to expand upon heating above a given temperature, depending on the chemistry of the shell copolymer. It is the shell that determines how and when the sphere will expand. In a particular embodiment of the present invention, EXPANCEL 091 DU 80 was expanded in the airlaid drying process. Other grades of EXPANCEL products (and other brands of expandable microspheres) may expand at lower or higher temperatures and may, thus, be suitable for engineered applications. Cooling causes the expanded microsphere shells to stiffen and thus remain in the expanded state. It is noted that the temperature range of the airlaid heating process governs the expansion of the microspheres. Desirably, suitable microspheres are selected by considering the temperature of the airlaid heating process.

Desirably, the amount of thermally expandable microspheres disposed in or on an airlaid substrate is from about 0.05 percent to about 20 percent based on the substrate basis weight. In another aspect, the microspheres disposed in or on an airlaid substrate is from about 0.5 percent to about 10 percent based on the substrate basis weight. In yet another aspect, the microspheres disposed in or on an airlaid substrate is from about 1 percent to about 5 percent based on the substrate basis weight.

In one example, absorbent cores are typically composed of superabsorbent particles and/or pulp. A newer class of absorbents also uses a binder to improve wet stability and to ease converting into final products. Binders can be liquid adhesive or thermally expandable fibers typically present in amounts between 10 and 25 weight percent.

The Airlaid Process

For an adhesive binder process, in one aspect of the invention the microspheres are sprayed onto one surface of the airlaid web before the adhesive binder(s) is applied to that surface. In another aspect of the invention, the binder(s) and microspheres are mixed and simultaneously applied to a surface of the airlaid web. In a further aspect of the invention, the microspheres are applied to the surface of the airlaid web after the adhesive binder(s) is applied to the same surface. In yet another aspect of the invention, the airlaid web is impregnated with microspheres during the forming of the airlaid web and the adhesive binder(s) is subsequently sprayed onto the impregnated web. The binder(s) and/or microspheres can be applied to both surfaces of the airlaid web in any combination or sequence.

FIG. 5 schematically illustrates an airlaying forming station useful for airlaying a web of fibers to make an airlaid sheet in accordance with the Example below.

If desired, there are different ways of imparting texture patterns to the tissue sheet for purposes of this invention. Fabric texture patterns associated with airlaying is one such method. The airlaying forming station 30 produces an airlaid web 32 on a forming fabric or screen 34. The forming fabric 34 can be in the form of an endless belt mounted on support rollers 36 and 38. A suitable driving device, such as an electric motor 40 rotates at least one of the support rollers 38 in a direction indicated by the arrows at a selected speed. As a result, the forming fabric 34 moves in a machine direction indicated by the arrow 42.

The forming fabric 34 can be provided in other forms as desired. For example, the forming fabric can be in the form of a circular drum which can be rotated using a motor as disclosed in U.S. Pat. No. 4,666,647, U.S. Pat. No. 4,761,258, or U.S. Pat. No. 6,202,259, which are incorporated herein by reference.

As shown, the airlaying forming station 30 includes a forming chamber 44 having end walls and side walls. Within the forming chamber 44 are a pair of material distributors 46 and 48 which distribute fibers and/or other particles inside the forming chamber 44 across the width of the chamber. The material distributors 46 and 48 can be, for instance, rotating cylindrical distributing screens.

In the embodiment shown in FIG. 5, a single forming chamber 44 is illustrated in association with the forming fabric 34. It should be understood, however, that more than one forming chamber can be included in the system. By including multiple forming chambers, layered webs can be formed in which each layer is made from the same or different materials.

Airlaying forming stations as shown in FIG. 5 are available commercially through Dan-Webforming Int. LTD. of Aarhus, Denmark. Other suitable airlaying forming systems are also available from M & J Fibretech of Horsens, Denmark. As described above, however, any suitable airlaying forming system can be used in accordance with the present invention.

As shown in FIG. 5, below the airlaying forming station 30 is a vacuum source 50, such as a conventional blower, for creating a selected pressure differential through the forming chamber 44 to draw the fibrous material against the forming fabric 34. If desired, a blower can also be incorporated into the forming chamber 44 for assisting in blowing the fibers down on to the forming fabric 34.

In one embodiment, the vacuum source 50 is a blower connected to a vacuum box 52 which is located below the forming chamber 44 and the forming fabric 34. The vacuum source 50 creates an airflow indicated by the arrows positioned within the forming chamber 44. Various seals can be used to increase the positive air pressure between the chamber and the forming fabric surface.

During operation, typically a fiber stock is fed to one or more defibrators (not shown) and fed to the material distributors 46 and 48. The material distributors distribute the fibers evenly throughout the forming chamber 44 as shown. Positive airflow created by the vacuum source 50 and possibly an additional blower force the fibers onto the forming fabric 34 thereby forming an airlaid non-woven web 32.

When wood pulp fibers are present in the airlaid web of the present invention, the pulp fibers may be in a rolled and fluffed form. As is known to those skilled in the art, fluffed fibers generally refer to fibers that have been shredded.

In one embodiment, the debonding agent can be an organic quaternary ammonium chloride and particularly a silicone based amine salt of a quaternary ammonium chloride. For example, the debonding agent can be PROSOFT TQ1003 marketed by the Hercules Corporation.

When forming the airlaid web 32 from different materials and fibers, the forming chamber 44 can include multiple inlets for feeding the materials to the chamber. Once in the chamber, the materials can be mixed together if desired. Alternatively, the different materials can be separated into different layers in forming the web.

Referring to FIG. 6, shown is a schematic diagram of an entire web forming system useful for making wipes in accordance with the present invention. In this embodiment, the system includes three separate airlaying forming chambers 44A and 44B and 44C. As described above, the use of multiple forming chambers can serve to facilitate formation of the airlaid web at a desired basis weight. Further, using multiple forming chambers can allow the formation of layered webs. As shown, forming stations 44A, 44B and 44C contribute to the formation of the airlaid web 32.

Airlaid web 32, after exiting the forming chambers 44A, 44B and 44C, is conveyed on a forming fabric 34 to a compaction device 54A. Compaction device 54A can be, for instance, a pair of opposing rolls that define a nip through which the airlaid web and forming fabric are passed. For example, in one embodiment, the compaction device can comprise a steel roll positioned above a rubber-coated roll. The compaction device moderately compacts the airlaid web to generate sufficient strength for transfer of the airlaid web to a transfer fabric such as, for instance, via an open gap arrangement. In general, the compaction device increases the density of the web over the entire surface area of the web as opposed to only creating localized high density areas.

After exiting the compaction device 54A, the airlaid web 32 is transferred to a transfer fabric 52. A suitable transfer fabric is ElectroTech 56 manufactured by Albany International. Once placed upon the transfer fabric, the airlaid web can be fed through a second compaction device 54B and further compacted against the transfer fabric to generate a texture pattern in the sheet. The compaction device 54B can also be used to improve the appearance of the web, to adjust the caliper of the web, and/or to increase the tensile strength of the web.

Next, the airlaid web 32 is transferred to a spray fabric 53A and fed to a spray chamber 56. Within the spray chamber 56, microspheres and binder(s) may be applied to the airlaid web. Under fabric vacuum may also be used to regulate and control penetration of the bonding material into the web. The binder(s) may add dry strength, wet strength, stretchability, and tear resistance. The expanded microspheres add bulk, resiliency, wet firmness and improved hand feel.

The bonding material and microspheres can be applied so as to uniformly cover the entire surface area of one side of the web. For instance, the bonding material and microspheres can be applied to the first side of the web so as to cover at least about 80% of the surface area of one side of the web, such as at least about 90% of the surface area of one side of the web. In other embodiments, the bonding material and microspheres can cover greater than about 95% of the surface area of one side of the web. It is possible that the microspheres will penetrate the web as seen in FIG. 4.

The bonding material and microspheres can be applied so as to cover only part of the entire surface area of one side of the web. This covered area can have certain patterns and designs disposed on the web, such as lines, circles, etc.

Once the binder(s) and microspheres are applied to at least one side of the web, as shown in FIG. 6, the airlaid web 32 is transferred to drying fabric 55A and fed to a drying apparatus 58. In the drying apparatus 58, the web is subjected to heat causing the bonding material and microspheres to dry and/or cure and cause the microspheres to expand. In one aspect, when using an ethylene vinyl acetate copolymer bonding material, the drying apparatus can be heated to a temperature of from about 120° C. to about 170° C.

The use of such expandable microspheres allows the opening up of the fiber structure so as to create a bulkier (i.e., less dense) web. Accordingly, when expandable microspheres are utilized in an airlaid product, the resulting airlaid product will have a bulkier structure than the same airlaid product at the same weight basis.

From the drying apparatus 58, the airlaid web is then transferred to a second spray fabric 53B and fed to a second spray chamber 60. In the spray chamber 60, a second bonding material is applied to the untreated side of the airlaid web. In general, the first bonding material and the second bonding material can be different bonding materials or the same bonding material. The second bonding material may be applied to the nonwoven web as described above with respect to the first bonding material.

From the second spray chamber 60, the nonwoven web is then transferred to a second drying fabric 55B and passed through a second drying apparatus 62 for drying and/or curing the second bonding material.

From the second drying apparatus 62, the airlaid web 32 is transferred to a return fabric 59 and may optionally be fed to a further compaction device 64 prior to being wound on a reel 66. The compaction device 64 can be similar to the first compaction device and may comprise, for instance, calendar rolls. Alternatively, the compaction device 64 can be a pair of embossing rolls used for the purpose of softening and further texturizing the sheet.

Wetting Composition for Wet Wipe Examples.

The wetting composition for use in combination with the dispersible ion-sensitive nonwoven materials may desirably comprise an aqueous composition containing insolubilizing agent that maintains the coherency of the binder composition, and thus, the in-use strength of the wet-wipe steady until the insolubilizing agent is diluted with sufficient water to provide strength loss.

Desirably, a salt triggerable binder composition may be insoluble in a wetting composition, wherein the wetting composition comprises at least about 0.3 weight percent of an insolubilizing agent which may be comprised of one or more inorganic and/or organic salts containing monovalent and/or divalent ions. More desirably, the binder composition may be insoluble in the wetting composition, wherein the wetting composition comprises from about 0.3% to about 10% by weight of an insolubilizing agent which may be comprised of one or more inorganic and/or organic salts containing monovalent and/or divalent ions. Even more desirably, the binder composition may be insoluble in the wetting composition, wherein the wetting composition comprises from about 0.5% to about 5% by weight of an insolubilizing agent which comprises one or more inorganic and/or organic salts containing monovalent and/or divalent ions. Most desirably, the binder composition may be insoluble in the wetting composition, wherein the wetting composition comprises from about 1.0% to about 4.0% by weight of an insolubilizing agent which comprises one or more inorganic and/or organic salts containing monovalent and/or divalent ions.

Suitable monovalent ions include, but are not limited to, Na⁺ ions, K+ ions, Li+ ions, NH₄+ ions, low molecular weight quaternary ammonium compounds (e.g., those having fewer than 5 carbons on any side groups), and a combination thereof. Suitable divalent ions include, but are not limited to, Zn²⁺, Ca²⁺ and Mg²⁺. These monovalent and divalent ions may be derived from organic and inorganic salts including, but not limited to, NaCl, NaBr, KCl, NH₄Cl, Na₂SO₄, ZnCl₂, CaCl₂, MgCl₂, MgSO₄, and combinations thereof. Typically, alkali metal halides are the most desirable monovalent or divalent ions because of cost, purity, low toxicity, and availability. A particularly desirable salt is NaCl.

The wetting composition may include a variety of additives or components, including those disclosed in U.S. Patent Publication No. 2002/0155281, which is hereby incorporated by reference in a manner that is consistent herewith. Possible additives may include, but are not limited to skin-care additives, odor control additives, wetting agents and/or cleaning agents; surfactants, pH control agents, preservatives and/or anti-microbial agents.

The wet wipes, as disclosed herein, do not require organic solvents to maintain in-use strength, and the wetting composition may be substantially free of organic solvents. However, a small amount of organic solvents may be included in the wetting composition for different purposes other than maintaining in-use wet strength.

After the airlaid substrate has been heated so that the microspheres expand, the wetting composition may be applied to the airlaid substrate in several ways (e.g. spraying or dipping).

General Procedures for Sample Preparation and Test Methods

Lab Preparation of Thermally-Bonded Airlaid Nonwoven Material Basesheets

A thermally-bonded airlaid (TBAL) nonwoven basesheet was prepared using Weyerhaeuser CF405 bleached softwood Kraft pulp fiber, available from Weyerhaeuser Company, Federal Way, Wash., and TENCEL® H400 945 synthetic fiber, available from Lenzing Group, Lenzing, Austria. The ratio of CF405 to TENCEL® is 85:15. In addition to the pulp and TENCEL®, thermal binder fiber is added to the air former to an overall level of 50% by weight. The thermal binder fiber used is a bicomponent core/sheath-type fiber available from ES FiberVisions Inc., located in Athens, Ga. The bicomponent fiber is a Polyethylene terephthalate-core/Polypropylene-sheath (PET-core/PP-sheath) with dimensions of 2.2 dtex and 6 mm fiber length. Enough materials are used in a laboratory-scale air former to prepare 50 gsm handsheets.

For codes that include thermally-expandable microspheres, EXPANCEL microspheres, available from Akzo Nobel, Sundsvall, Sweden, were also added to the air former, in addition to the pulp and TENCEL®.

The resulting lab-prepared TBAL basesheet is then compressed using a heated Carver press, model 4531, available from Carver, Inc., located in Wabash, Ind. The compression force is set to 30000 lb and the temperature of the plates is set to 175 degrees F., for duration of 1 minute.

Lab Preparation of Adhesively-Bonded Airlaid Nonwoven Material Basesheets

Basesheets of the nonwoven web, used to prepare samples of adhesively-bonded airlaid (ABAL), were produced on a Dan-Web pilot line, available from Dan-Web, Risskov, Denmark. The un-bonded basesheet was prepared using Weyerhaeuser CF405 bleached softwood Kraft pulp fiber, available from Weyerhaeuser Company, Federal Way, Wash., and TENCEL® H400 945 synthetic fiber, available from Lenzing Group, Lenzing, Austria. The ratio of CF405 to TENCEL® is 85:15. The basis weight of this material is 58.5 gsm.

Aqueous adhesive binder solutions are then topically applied to both sides of the un-bonded airlaid basesheet. The binder solutions can be dispersible or non-dispersible in nature. First, the basesheet is placed on a screen which is under vacuum conditions during the spraying operation. Then the basesheet is sprayed on each side equally to achieve a final binder add-on of 18 to 20% by weight, in the handsheet. The binder composition is typically approximately 15 to 16% solids level. A Quick VEEJET® nozzle, type 8001, manufactured by Spraying Systems Co., Wheaton, Ill., operating at approximately 80 psi was employed to spray the binder composition onto the fibrous material. The distance from the nozzle tip to the basesheet is 8 inches.

For codes that include thermally-expandable microspheres, EXPANCEL microspheres, available from Akzo Nobel, Sundsvall, Sweden, were also sprayed onto the basesheet, either before, in combination with, or after, the adhesive binder solution, depending on the sample code.

The resulting adhesive binder-sprayed airlaid basesheet is then transferred to and dried in a Werner Mathis Model LTV Through-Air Dryer, available from Mathis AG, located in Oberhasli, Switzerland. The Through-Air Dryer is set to 180 degrees C. for 23 seconds at 100% fan speed.

Lab Preparation of Multi-Bonded (Thermally and Adhesively) Airlaid Nonwoven

Material Basesheets

Multi-bonded airlaid (MBAL) nonwoven basesheet was prepared using Weyerhaeuser CF405 bleached softwood Kraft pulp fiber, available from Weyerhaeuser Company, Federal Way, Wash., and TENCEL® H400 945 synthetic fiber, available from Lenzing Group, Lenzing, Austria. The ratio of CF405 to TENCEL® is 85:15. In addition to the pulp and TENCEL®, thermal binder fiber is added to the air former to an overall level of 20% by weight. The thermal binder fiber used is a bicomponent core/sheath-type fiber available from ES FiberVisions Inc., located in Athens, Ga. The bicomponent fiber is a polyethylene terephthalate-core/polypropylene-sheath (PET-core/PP-sheath) with dimensions of 2.2 dtex and 6 mm fiber length. Enough materials are used in a laboratory-scale air former to prepare 50 gsm handsheets.

The resulting lab-prepared basesheet is then compressed using a heated Carver press, model 4531, available from Carver, Inc., located in Wabash, Ind. The compression force is set to 15000 lb and the temperature of the plates is set to 175 degrees F., for duration of 1 minute.

Aqueous adhesive binder solutions are then topically applied to both sides of the airlaid basesheet. First, the basesheet is placed on a screen which is under vacuum conditions during the spraying operation. Then the basesheet is sprayed on each side equally to achieve a final binder add-on of 18 to 20% by weight, in the handsheet. The binder composition is typically approximately 15 to 16% solids level. A Quick VEEJET® nozzle, type 8001, manufactured by Spraying Systems Co., Wheaton, Ill., operating at approximately 80 psi was employed to spray the binder composition onto the fibrous material. The distance from the nozzle tip to the basesheet is 8 inches.

For codes that include thermally-expandable microspheres, EXPANCEL microspheres, available from Akzo Nobel, Sundsvall, Sweden, were also sprayed onto the basesheet, either before, in combination with, or after, the adhesive binder solution, depending on the sample code.

The resulting adhesive binder-sprayed airlaid basesheet is then transferred to and dried in a Werner Mathis Model LTV Through-Air Dryer, available from Mathis AG, located in Oberhasli, Switzerland. The Through-Air Dryer is set to 180 degrees C. for 23 seconds at 100% fan speed.

Lab-Prepared Wet Wipe Preparation Protocol

Each 10″×13″ lab-prepared airlaid nonwoven material was die-cut into two 7.5″×5.5″ dry wipes, with the shorter direction being the machine-direction (MD) direction. Each dry wipe was then sprayed with a 235% add-on of a wetting composition that is used on commercially available wet wipes under the trade designation KLEENEX® COTTONELLE FRESH® Folded Wipes (Kimberly-Clark Corporation of Neenah, Wis.) containing 2 wt % sodium chloride to yield lab-prepared wet wipes. A stack of 10 lab-prepared wet wipes was formed and placed inside a re-sealable plastic bag. The stack of 10 lab-prepared wet wipes in the re-sealable plastic bag was compressed with a 22 lb metal roller, where the open bag containing the wipes is rolled four times each in both the MD and cross-direction (CD). The bag is sealed and then compressed under 1000 g of weight for 48 hours.

Lab-Prepared Dry Wipe Preparation Protocol

Each 10″×13″ lab-prepared airlaid nonwoven material was die cut into two 7.5″×5.5″ dry wipes, with the shorter direction being the machine-direction (MD) direction. The wipes are then conditioned at 23 degrees C. and 50% relative humidity.

Wet or Dry Wipe Caliper (Thickness) Measurements

As used herein, the “thickness” of a web is measured with a 3-inch diameter, ⅝″ thick, acrylic plastic disk connected to the spindle of a SONY Digital Indicator U60A (SONY Corporation, Tokyo, Japan) and which delivers a net load of 0.05 psi to the sample being measured. The SONY Digital Indicator is zeroed when the disk rests on a flat surface. When a sample having a size at least as great as the acrylic disk is placed under the disk, a thickness reading can be obtained from the digital readout of the indicator. Stacks of 10 wet or dry wipes are measured in this manner with three replicates and averaged. The average is divided by 10 to obtain a caliper on a per-sheet basis.

Bone Dry Basis Weight Measurements

Bone Dry Basis Weight measurements were taken by weighing the basesheet samples immediately after removal from the Through-Air Dryer or the Carver Press, at the completion of the lab preparation process. The sample weights were then converted to grams per square meter (gsm) values.

EXAMPLES Example 1 TBAL

Thermally-bonded airlaid (TBAL) basesheets were prepared as described in the section “Lab Preparation of Thermally-Bonded Airlaid Nonwoven Material Basesheets”.

Samples were made with and without EXPANCEL thermally-expandable microspheres. The type of EXPANCEL used for these samples was “009 DU 80”, available from Akzo Nobel, Sundsvall, Sweden.

Additionally, Dry and Wet Wipe samples were prepared from these TBAL basesheets as described in the sections “Lab-Prepared Dry Wipe Preparation Protocol” and “Lab-Prepared Wet Wipe Preparation Protocol.”

These samples are coded A1, A2, A3, and A4. Pertinent information related to their composition is described in Table 1.

TABLE 1 Type Type of Type of Type of Wt % Wt % Dry of Thermal Adhesive EXPANCEL Thermal Adhesive Wt % Wt % Wt % or Code Airlaid Binder Binder microspheres Binder Binder CF405 TENCEL EXPANCEL Wet A1 TBAL bico PET- NA NA 50 0 42.5 7.5 0 Dry core/PP- sheath A2 TBAL bico PET- NA 009 DU 80 45.4 0 38.6 6.8 9.1 Dry core/PP- sheath A3 TBAL bico PET- NA NA 50 0 42.5 7.5 0 Wet core/PP- sheath A4 TBAL bico PET- NA 009 DU 80 45.4 0 38.6 6.8 9.1 Wet core/PP- sheath

Stacks of 10 wet or dry wipes were then measured as described in the section “Wet or Dry Wipe Caliper (Thickness) Measurements”. This resulted in single sheet calipers after dividing the average measurements by 10. Additionally, the single sheet bulk can be calculated as the quotient of the single sheet caliper, expressed in microns, divided by the bone dry basis weight, expressed in grams per square meter (gsm). The resulting sheet bulk is expressed in cubic centimeters per gram. This allows the calipers to be compared after being normalized by basis weight. This information is detailed in Table 2.

TABLE 2 Overall Bone Dry Single Sheet Sheet Bulk % Thickness Code Basis Weight (gsm) Caliper (mm) (cc/g) Improvement A1 50 0.93 18.6 NA A2 55 1.49 27.1 45.7 A3 50 0.49 9.8 NA A4 55 0.85 15.5 57.7

As can be seen, the sheet bulk increases by 45.7% for the dry TBAL wipes, while the sheet bulk increases by 57.7% for the wet TBAL wipes.

Example 2 MBAL

Multi-bonded airlaid (MBAL) basesheets were prepared as described in the section “Lab Preparation of Multi-Bonded (Thermally and Adhesively) Airlaid Nonwoven Material Basesheets”. The adhesive binder was an ion-sensitive dispersible binder composition, comprising a 70/30 combination of binder and co-binder mixed with de-ionized water to a solids level of 15.5%.

The binder was a cationic ion-sensitive polyacrylate. More specifically, the cationic ion-sensitive polyacrylate is a copolymer of methyl acrylate (96 mol %) and [(2-acryloyloxy)ethyl]trimethyl ammonium chloride (4 mol %) with a weight average molecular weight between 140,000 to 200,000 g/mol as determined by gel permeation chromatography in a dimethylformamide/LiCl mobile phase. The co-binder was VINNAPAS® EZ123 (formerly known as AIRFLEX® EZ123), available from Wacker Chemie AG, Munich, Germany.

Samples were made with and without EXPANCEL thermally-expandable microspheres. The type of EXPANCEL used for these samples are “091 DU 80”, available from Akzo Nobel, Sundsvall, Sweden. These were mixed into the binder composition prior to spraying on the basesheet samples.

Additionally, Dry and Wet Wipe samples were prepared from these MBAL basesheets as described in the sections “Lab-Prepared Dry Wipe Preparation Protocol” and “Lab-Prepared Wet Wipe Preparation Protocol”.

These samples are coded B1, B2, B3, and B4. Pertinent information related to their composition is described in Table 3.

TABLE 3 Type Type of Type of Type of Wt % Wt % Dry of Thermal Adhesive EXPANCEL Thermal Adhesive Wt % Wt % Wt % or Code Airlaid Binder Binder microspheres Binder Binder CF405 TENCEL EXPANCEL Wet B1 MBAL bico PET- Dispersible NA 16.4 18 55.7 9.8 0 Dry core/PP- sheath B2 MBAL bico PET- Dispersible 091 DU 80 15.4 18 52.4 9.2 4.9 Dry core/PP- sheath B3 MBAL bico PET- Dispersible NA 16.4 18 55.7 9.8 0 Wet core/PP- sheath B4 MBAL bico PET- Dispersible 091 DU 80 15.4 18 52.4 9.2 4.9 Wet core/PP- sheath

Stacks of 10 wet or dry wipes were then measured as described in the section “Wet or Dry Wipe Caliper (Thickness) Measurements.” This resulted in single sheet calipers after dividing the average measurements by 10. Additionally, the single sheet bulk can be calculated as the quotient of the single sheet caliper, expressed in microns, divided by the bone dry basis weight, expressed in grams per sqare meter (gsm). The resulting sheet bulk is express in cubic centimeters per gram. This allows the calipers to be compared after being normalized by basis weight. This information is detailed in Table 4.

TABLE 4 Overall Bone Dry Single Sheet Sheet Bulk % Thickness Code Basis Weight (gsm) Caliper (mm) (cc/g) Improvement B1 61 0.92 15.1 NA B2 64.9 1.76 27.1  79.8 B3 61 0.34 5.6 NA B4 64.9 0.84 12.9 132.2

As can be seen, the sheet bulk increases by 79.8% for the dry MBAL wipes, while the caliper/bdbwt increases by 132.2% for the wet MBAL wipes.

Example 3 ABAL Dispersible

Adhesively-bonded airlaid (ABAL) basesheets were prepared as described in the section “Lab Preparation of Adhesively-Bonded Airlaid Nonwoven Material Basesheets”. The adhesive binder was an ion-sensitive dispersible binder composition, comprising a 70/30 combination of binder and co-binder mixed with de-ionized water to a solids level of 15.5%.

The binder was a cationic ion-sensitive polyacrylate. More specifically, the cationic ion-sensitive polyacrylate is a copolymer of methyl acrylate (96 mol %) and [(2-acryloyloxy)ethyl]trimethyl ammonium chloride (4 mol %) with a weight average molecular weight between 140,000 to 200,000 g/mol as determined by gel permeation chromatography in a dimethylformamide/LiCl mobile phase. The co-binder was VINNAPAS® EZ123 (formerly known as AIRFLEX® EZ123), available from Wacker Chemie AG, Munich, Germany.

Samples were made with and without EXPANCEL thermally-expandable microspheres. The type of EXPANCEL used for these samples are “009 DU 80”, available from Akzo Nobel, Sundsvall, Sweden. These were mixed into the binder composition prior to spraying on the basesheet samples.

Additionally, Dry and Wet Wipe samples were prepared from these dispersible ABAL basesheets as described in the sections “Lab-Prepared Dry Wipe Preparation Protocol” and “Lab-Prepared Wet Wipe Preparation Protocol.”

These samples are coded C1, C2, C3, . . . , C12. Pertinent information related to their composition is described in Table 5.

TABLE 5 Type Type of Type of Type of Wt % Wt % Dry of Thermal Adhesive EXPANCEL Thermal Adhesive Wt % Wt % Wt % or Code Airlaid Binder Binder microspheres Binder Binder CF405 TENCEL EXPANCEL Wet C1 ABAL NA Dispersible NA 0 18 69.7 12.3 0.0 Dry C2 ABAL NA Dispersible 009 DU 80 0 18 68.9 12.2 1.0 Dry C3 ABAL NA Dispersible 009 DU 80 0 18 68.0 12.0 2.0 Dry C4 ABAL NA Dispersible 009 DU 80 0 18 67.2 11.9 3.0 Dry C5 ABAL NA Dispersible 009 DU 80 0 18 66.3 11.7 4.0 Dry C6 ABAL NA Dispersible 009 DU 80 0 18 65.5 11.6 5.0 Dry C7 ABAL NA Dispersible NA 0 18 69.7 12.3 0.0 Wet C8 ABAL NA Dispersible 009 DU 80 0 18 68.9 12.2 1.0 Wet C9 ABAL NA Dispersible 009 DU 80 0 18 68.0 12.0 2.0 Wet C10 ABAL NA Dispersible 009 DU 80 0 18 67.2 11.9 3.0 Wet C11 ABAL NA Dispersible 009 DU 80 0 18 66.3 11.7 4.0 Wet C12 ABAL NA Dispersible 009 DU 80 0 18 65.5 11.6 5.0 Wet

Stacks of 10 wet or dry wipes were then measured as described in the section “Wet or Dry Wipe Caliper (Thickness) Measurements”. This resulted in single sheet calipers after dividing the average measurements by 10. Additionally, the single sheet bulk can be calculated as the quotient of the single sheet caliper, expressed in microns, divided by the bone dry basis weight, expressed in grams per square meter (gsm). The resulting sheet bulk is expressed in cubic centimeters per gram. This allows the calipers to be compared after being normalized by basis weight. This information is detailed in Table 6.

TABLE 6 Overall Bone Dry Single Sheet Sheet Bulk % Thickness Code Basis Weight (gsm) Caliper (mm) (cc/g) Improvement C1 67.1 1.11 16.5 NA C2 67.9 1.33 19.6 18.4 C3 68.8 1.56 22.7 37.1 C4 69.6 1.80 25.9 56.3 C5 70.5 2.06 29.2 76.6 C6 71.4 2.17 30.4 83.7 C7 67.1 0.37 5.5 NA C8 67.9 0.42 6.2 12.2 C9 68.8 0.53 7.7 39.7 C10 69.6 0.65 9.3 69.4 C11 70.5 0.80 11.3 105.8 C12 71.4 0.81 11.3 105.7

As can be seen, the sheet bulk increases from 18.4% to 83.7% for the dry dispersible ABAL wipes, depending on the amount of EXPANCEL added to the basesheet, while the sheet bulk increases from 12.2% to 105.8% for the wet dispersible ABAL wipes.

The moist wipes corresponding to code C12 were imaged by SEM to investigate the distribution of expanded microspheres in the wipes. Code C7, which did not contain any microspheres, were also imaged by SEM to represent a “control” code.

FIGS. 1 and 2 show the SEM images of the control code C7 in cross-section and on the surface, respectively. There are no microspheres in this code and the sheet is thin and compact.

FIGS. 3 and 4 show the SEM images of code C12 in the cross-section and on the surface, respectively. This code includes expanded microspheres and it can be observed that the microspheres are well-distributed in both the planar x-y surface and the z-direction thickness.

Example 4 ABAL Non-Dispersible

Adhesively-bonded airlaid (ABAL) basesheets were prepared as described in the section “Lab Preparation of Adhesively-Bonded Airlaid Nonwoven Material Basesheets.” The adhesive binder was a non-dispersible binder composition, comprising a non-dispersible binder mixed with de-ionized water to a solids level of 15.5%. The binder was VINNAPAS® 192 available from Wacker Chemie AG, Munich, Germany.

Samples were made with and without EXPANCEL thermally-expandable microspheres. The type of EXPANCEL used for these samples are “091 DU 80”, available from Akzo Nobel, Sundsvall, Sweden. These were mixed into the binder composition prior to spraying on the basesheet samples.

Additionally, Dry and Wet Wipe samples were prepared from these non-dispersible ABAL basesheets as described in the sections “Lab-Prepared Dry Wipe Preparation Protocol” and “Lab-Prepared Wet Wipe Preparation Protocol”. These samples are coded D1, D2, D3, . . . , D12. Pertinent information related to their composition is described in Table 7.

TABLE 7 Type Type of Type of Type of Wt % Wt % Dry of Thermal Adhesive EXPANCEL Thermal Adhesive Wt % Wt % Wt % or Code Airlaid Binder Binder microspheres Binder Binder CF405 TENCEL EXPANCEL Wet D1 ABAL NA Non- NA 0 18 69.7 12.3 0.0 Dry dispersible D2 ABAL NA Non- 091 DU 80 0 18 68.9 12.2 1.0 Dry dispersible D3 ABAL NA Non- 091 DU 80 0 18 68.0 12.0 2.0 Dry dispersible D4 ABAL NA Non- 091 DU 80 0 18 67.2 11.9 3.0 Dry dispersible D5 ABAL NA Non- 091 DU 80 0 18 66.3 11.7 4.0 Dry dispersible D6 ABAL NA Non- 091 DU 80 0 18 65.5 11.6 5.0 Dry dispersible D7 ABAL NA Non- NA 0 18 69.7 12.3 0.0 Wet dispersible D8 ABAL NA Non- 091 DU 80 0 18 68.9 12.2 1.0 Wet dispersible D9 ABAL NA Non- 091 DU 80 0 18 68.0 12.0 2.0 Wet dispersible D10 ABAL NA Non- 091 DU 80 0 18 67.2 11.9 3.0 Wet dispersible D11 ABAL NA Non- 091 DU 80 0 18 66.3 11.7 4.0 Wet dispersible D12 ABAL NA Non- 091 DU 80 0 18 65.5 11.6 5.0 Wet dispersible

Stacks of 10 wet or dry wipes were then measured as described in the section “Wet or Dry Wipe Caliper (Thickness) Measurements.” This resulted in single sheet calipers after dividing the average measurements by 10. Additionally, single sheet bulk can be calculated as the quotient of the single sheet caliper, expressed in microns, divided by the bone dry basis weight, expressed in grams per square meter (gsm). The resulting sheet bulk is expressed in cubic centimeters per gram. This allows the calipers to be compared after being normalized by basis weight. This information is detailed in Table 8.

TABLE 8 Overall Bone Dry Single Sheet Sheet Bulk % Thickness Code Basis Weight (gsm) Caliper (mm) (cc/g) Improvement D1 67.1 1.13 16.8 NA D2 67.9 1.28 18.9 11.9 D3 68.8 1.38 20.1 19.1 D4 69.6 1.46 21.0 24.6 D5 70.5 1.58 22.4 33.1 D6 71.4 1.56 21.8 29.7 D7 67.1 0.44 6.6 NA D8 67.9 0.61 9.0 37.0 D9 68.8 0.71 10.3 57.4 D10 69.6 0.80 11.5 75.3 D11 70.5 0.98 13.9 112.0 D12 71.4 1.02 14.3 117.9

As can be seen, the sheet bulk increases from 11.9% to 33.1% for the dry non-dispersible ABAL wipes, depending on the amount of EXPANCEL added to the basesheet, while the sheet bulk increases from 37.0% to 117.9% for the wet non-dispersible ABAL wipes.

Overall Results

As can be seen from the combined data from the above examples, the addition of EXPANCEL thermally-expandable microspheres increases the thickness of wet wipes by at least about 12%, when added at the 1% level, to as much as about 132%, when added at the 5% level. 

1. A sheet comprising: an airlaid material having a thickness and comprising fibers; a plurality of thermally expandable microspheres distributed at least partially through the material thickness; and a binder material applied to the sheet.
 2. The sheet of claim 1 wherein the microspheres have an initial state and an expanded state, wherein the microspheres have an average diameter of about 80 micrometers when in the expanded state.
 3. The sheet of claim 1 wherein the total adhesive binder material within the sheet is about 15 to 20 percent by weight.
 4. The sheet of claim 3 wherein the thermally expandable microspheres content in the sheet is about 1 to about 10 percent by weight.
 5. The sheet of claim 4 wherein the sheet is a thermally-bonded airlaid in the form of a wet wipe, the sheet having about a 46 to about 58 percent increase in sheet bulk as determined by the caliper measurement and bone-dry basis-weight test methods as described herein.
 6. The sheet of claim 5 wherein the sheet is a multi-bonded airlaid material in the form of a wet wipe, wherein the wet wipe has about 80 to about 132 percent increase in sheet bulk as determined by the caliper measurement and bone-dry basis-weight test methods as described herein, and wherein the multi-bonded airlaid further comprises a thermal binder of about 16 percent by weight.
 7. The sheet of claim 5 wherein the sheet is an adhesively-bonded airlaid in the form of a dispersible wet wipe, the sheet with 1 to 5% thermally expandable micropsheres by weight, and having about 10 to about 110 percent increase in sheet bulk as determined by the caliper measurement and bone-dry basis-weight test methods as described herein.
 8. The sheet of claim 1 wherein the sheet is an adhesively-bonded airlaid in the form of a non-dispersible wet wipe, the sheet with 1 to 5% thermally expandable microspheres by weight and having about a 35 to about 120 percent increase in sheet bulk as determined by the caliper measurement and bone-dry basis-weight test methods as described herein.
 9. The sheet of claim 1 wherein the binder is salt responsive.
 10. The sheet of claim 1 wherein the binder is water dispersible.
 11. A method of making an airlaid sheet having a thickness, the method comprising the steps of: (a) spraying an airlaid sheet with a bonding material; and (b) spraying the thermally expandable microspheres onto the airlaid sheet.
 12. The method of claim 11 further comprising the step of applying a vacuum to the sheet so that the microspheres are distributed at least partially through the sheet thickness.
 13. The method of claim 11 wherein step (b) is performed before step (a).
 14. The method of claim 11 wherein steps (a) and (b) are accomplished simultaneously by mixing the bonding material with the thermally expandable microspheres prior to the spraying step.
 15. A method of making an airlaid sheet comprising the step of disposing the thermally expandable microspheres and fibers for airlaying into a forming station so that the airlaid sheet has thermally expandable microspheres distributed throughout the sheet thickness prior to spraying the sheet with a binder.
 16. The method of claim 15 wherein the thermally expandable microspheres have an average diameter of about 80 micrometers when in an expanded state.
 17. The method of claim 16 comprising the step of heating the sheet after distributing the thermally expandable microspheres into the sheet so that the microspheres expand to the average diameter. 